Recovery of rubberlike products from emulsions



UNITED] STATE to that of cottage cheese.

I ulated material tends to see, was

RECOVERY oF RUBBERLIKE PRODUCTS FROM EMULSIONS Robert R. Dreisbach,Midland, The Dow Chemical Company,

corporation of Michigan Application April 14, 1942, Serial No 438,874

5 Claims.

This invention concerns an improved method for the recovery of syntheticsolid rubber-like cyanide, styrene, methyl vinyl ketone, or methylisopropenyl ketone, etc., while in aqueous emulsion. The resultantemulsion of the product resembles natural rubber latex and the productmay be recovered therefrom by procedures similar to those employed inrecovering natural rubber from its latex. In the commercial productionof rubber, the usual procedure is to treat the latex with a small amountof a stabilizer, i. e. an anti-oxidant, and then to treat the latex in avat with a coagulating agent such as formic or aceticacid, whereby therubber separates from the emulsion 1n the form of a water-logged lump ormass. The mass is liftedfrom the vat, cut when necessary into pieces ofsize suitable for feeding to rolls, and is washed with water duringpassage through the rolls, after which it is further rolled to press thesame into a form which will permit fairly rapid drying and which issuitable for subsequent packing for shipment. The

rolls are usually designed and operated to produce rubber sheeting orcrepe which is suspended fromracks and is air-dried for several days ata moderately elevated temperature, e. g. about 50 C., so asto avoid thestretching or tearing which might occur at higher drying temperatures.Drying is usually continued until the water content of the product isreduced to between 20 and 30 per cent by weight. This usual method istimeconsuming and requiresmuch manual labor.

It is an object of this invention to provide a method whereby therecovery of rubber-like products-fromemulsions may be accomplishedrapidly and with a minimum of labor. Other objects'will be apparent'from the following description of the invention. y r

I have found that by vigorously stirring a synthetic latex duringaddition of a coagulating agent thereto, the rubber-like, product may becaused to coagulate in the form of smallirregularly shaped pieces havingan appearance similar 7 It is important that the stirring be vigoroussince otherwise the coagrise and collect at the surface of the mixturewhere the pieces rapidly coalesce or become cemented together as a po-Mich., assignor to Midland, Mich., a

rous mass which is poorly suited for further handling. However, bycontinuously feeding the emulsion and the coagulating agent into thecon- I tainer until the latter is filled to overflowing,

-while' at the same time vigorously stirring the mixture, the bits ofcoagulated product are distributed throughout the mixture and areprevented from adhering together and are carried from the container at,a substantially uniform rate by the overflowing liquid. a

I have also found that the loose product thus obtained is well suited tosubsequent handling,

. manner.

e. g. drying in continuous or semi-continuous Although the bits of wetproduct, if permitted to stand without agitation for only a short time,e. g., 10 minutes or longer, tend to cement together with formation of aporous mass,

' this tendency is lessened as the productis dried.

, when such'cohesion of the product does occur, the cohesive forcesbetween By promptly draining excess water from the product as itoverflows from the coagulation chamber and pressing additional waterfrom the product, e. g. with rolls, the tendency for the granules toadhere to one another is reduced and the product may be permitted tostand in thin be ds. e. g. of less than one foot thickness, for sometime, e. g. one hour or longer, before appreciable cohesion of thegranules occurs. Furthermore, bits of partially dried the particlesmaking up the resultant porous mass are usually quite weak so that thematerial may again be granulated by passage through a shredding machineor similar device for tearing the granules apart from one another.

I have further found that the partially dried granular product may quiterapidly be further dried at temperatures higher than are suitable forthe drying of sheet or crepe rubber, and that such further drying mayadvantageously be carried out in a rotating vacuum oven having smoothand curved interior surfaces. If the drying at elevated temperatures iscarried out on stationary trays or pans, the granules of product becomecemented together with formation of a porous mass. If during finaldrying the product is agitated-by means of blades, e. g. by stirring thesame with a blade-likedevice or by drying the product in a rotating ovenhaving internal baflles or blade-like projections, the product occludesto the blades with formation of a rubbery mass which is difficult toremove. By carrying out the final drying in a rotating oven havingsmooth internal surfaces, the granules uct do not become matted togetheror occlude to the oven surfaces, so that the dried product of prodisreadily discharged from the oven and is obtained in granular form. Afterbeing dried, e. g. to a moisture content of less than two per cent byweight, the granules may be stored at room temperature in beds of lessthan one foot depth for several days without becoming cemented together.However, the dried granular product may readily be molded, e. g. pressedor rolled, at room temperature or at elevated temperatures, into uniformblocks, sheets or crepe suitable for shipment.

On the basis of the discoveries just mentioned, I have devised thefollowing improved method for the recovery of rubber-like products fromemulsions.

The accompanying drawing is a diagrammatic sketch showing an arrangementof apparatus suitable for use in practicing the invention. In thedrawing the numeral designates a rotating autoclave, or tumbler, havingsmooth curved internal surfaces. The autoclave is provided with asurrounding jacket 2 through which water, air or other heating orcooling fluid may be passed. The bearing blocks 3 and 4, which supportthe respective shafts 5 and B projecting lengthwise from the oppositeends of the autoclave, are hollowed so as to form the annular spaces 7and 8 about the shafts. A fluid inlet 9 connects with the annular spaceI and a fluid outlet l leads from the other annular space 3. The jacket2 of the autoclave is provided at its opposite ends with the sleeves iiand i2 which project about the respective shafts and 6 part way into thebearing blocks 3 and 4, thus forming a continuous opening so that afluid introduced at inlet 9 will flow through the jacket 2 surroundingthe autoclave and will flow from the apparatus through outlet l0.

The autoclave is also provided with the projecting valved pipes l3 andI4. Pipe I3 is fitted as indicated with a half of a pipe union and maybe connected with either the inlet line l5 or an outlet line I6, each ofwhich lines is provided with a half-union capable of being mated withthat on pipe |2 to form a full union.

Line |6 leads to a storage tank H which may be provided with anotherinlet line 8 for the introduction of a stabilizing agent. .A valved linethe bin 35 is a rotatable vacuum drying oven 31 having smooth curvedinternal surfaces. The manhole 38 of oven 31, which manhole is providedwith a hinged lid 39, is situated below the I9 leads from tank IT to acoagulation chamber 20. The latter is also provided with a valved vinletline 2| which leads from another storage tank 22. A mechanical stirrer23 projects into the chamber 20. Toward the top of chamber 20 is anoverflow trough or flume 24 which is positioned so as to dischargematerial overflowing from chamber 20 onto a moving perforated belt 25,which may be constructed of metal screening. The belt 25 is supported bythe pulleys 26 and 21, one or both of which may be actuated by usualmeans, not shown. The belt 25 passes between the rollers 28 and 29 whichare preferably constructed of rubber or other soft, resilient materialand which are positioned so as to firmly press the belt 25 between thesame. The rollers 28 and 29 may be actuated by the lengthwise movementof the belt 25, but they are preferably driven by other usual means notshown, e. g. a belt orchain, at a rate corresponding to the movement ofthe belt 25.

The pulley 21, supporting the belt 25, is posi-.

tioned above a pair of steel.or other metal rollers 30 and 3| so thatsolids which drop from belt 25 will be fed between the rollers. Therollers 3|] and 3| are closely positioned, face to face, and are rotatedby usual means not shown.

outlet 36 to the bin 35 so that material from the bin may be chargeddirectly into the oven. The oven 31 is provided with a surroundingjacket 4|) through which a heating fluid such as water, steam or air,etc., may be passed. The shafts 3| and 42 project from the opposite endsof oven 31 through the respective bearing blocks 43 and 44. The shaft 42is provided with a central bore 45 through which vapors may be withdrawnfrom the oven. The jacket 40 to oven 31 is provided at its opposite endswith the sleeves 46 and 37 which project about the respective shafts 4iand 42 to the respective cavities 48 and 49 in the bearing blocks 43 and44. A fluid inlet 50 leads to the cavity 48 in bearing block 43 'and anoutlet 5| leads from the cavity 69 in bearing block 3 3. Channels arethus provided whereby a heating fluid may be fed to and withdrawn fromthe annular space between the oven 37 and its surrounding jacket 40. Atthe end of shaft 42 the bearing block 44 is fitted to a vapor line 52which leads to a vacuum pump, not shown.

In producing a synthetic rubber using the apparatus illustrated in thedrawing, an emulsion of the compound or compounds to be polymerized, orthe ingredients necessary to form such emulsion, are charged intoautoclave I through the inlet line I5 and pipe I3, after which thevalves in pipe l3 and line l5 are closed and these lines aredisconnected. As is well known, the starting materials used in formingsuch an emulsion comprise, as the essential ingredients, a conjugateddiolefine or a mixture of a conjugated diolefine and one or more otherunsaturated organic compounds capable of being co-polymerized therewith,water, an emulsifying agent, and preferably a per-oxygen compound suchas hydrogen peroxide, sodium, potassium, or ammonium persulphate, orsodium, potassium, or ammonium perborate, etc., as a catalyst for thepolymerization. In many instances acids, alkalies, or bufiering agentsare also added so as to obtain the pH value at which a particularpolymerization occurs most favorably. Examples of polymerizable organiccompounds which may be used as starting materials are butadiene-1.3,isoprene, 2.3-dimethyl-butadiene-1.3, mixtures .of butadiene- 1.3 andstyrene, mixtures of butadiene-LB and vinyl cyanide, mixtures ofbutadiene-1.3 and either methyl vinyl ketone or methyl isopropenylketone, mixtures of isoprene and styrene,

- a heating fluid, usually warm water, 15

13 and H are i let l8. The proportion of conveniently be washed withfresh waterprior as lauryi and myristic alcohols, alkali salts of higheralcohol mono-esters of sulphuric acid, sulphonates and sulphonic acidderivatives of alkyl substituted aromatic hydrocarbons, egg albumen,blood serum, etc. The proportions in which the several startingmaterials may be employed are known to the art and in most instances maybe varied widely, the preferred proportions depending upon the physicaland mechanical properties desired in the rubber-like product. Afterbeing charged, the autoclave is rotated and introduced through inlet 9.flows through annular space 1 between-the shell l and the jacket 2. ofthe autoclave, into annular space 8 and flows from the latterthroughoutlet ID. The water is usually heated to about 55-65" C. so asto bring the reaction mixture temperature, but the polymerization may becar ried out at lower or higher temperatures, e. g. at temperaturesranging from room temperature to 100 C. or higher. The time required forcompletion of the reaction varies from several hours to severaldays orlonger, depending upon the particular compounds being polymerized andthe catalyst and other reaction conditions employed. When thepolymerization is completed, rotation of the autoclave is discontinuedand pipe 53 is connected with line B6. The valves in pipes then openedso as to permit flow of the emulsion from the autoclave l to the storagetank 11. ,An agent. such as phenyl betanaphthylamine, di-(para-hydroxyphenyl) cyclohexane, Antox (a condensation product of aniline andbutyraldehyde) or any of the other antioxidants usually employed asstabilizers for natural rubber, is preferably added, e. g. throughinantioxidant required varies, depending upon the particular agent used,but it is usually employed in amount corresponding to between 0.5 and 2per cent of the dry weight of the rubber-like product. It will beunderstood, 0! course, that tank 11 may'serve as a storage vessel forthe emulsified, product from a plurality of autoclaves and that bypropdifferent autoif dethe discharge of the erly timing tank H, theantioxidant may,

claves into sired, be added continuously emulsion may be withdrawncontinuously from the tank.

The valvein line i9 is opened sufficiently to permit steady flow of theemulsion from tank i! into the coagulation chamber it. Whilecontinuingflow of the emulsion to chamber 20, a coagulating agent isintroduced in steady flow from the storage tank 22 through line 2| andthe stirrer 23 is rotated at sufficient speed to cause the rubber-likeproduct to coagulate in the form of small irregular shaped pieces havingan apto that of cottage cheese. As agent 1 preferably employ a dilute,e. g. 0.5 to 1 per-cent aqueous solution of calcium chloride, but inother concentrations known coagulating agents, e. g. aqueous solutionsof salts such as sodium chloride, sodium sulphate, ammonium chloride,.barium chloride, aluminum and the treated to passage through saidrollers, but this is not required.

During travel of the belt 25 over pulley 21, the product drops from thebelt and falls between the rotating metal rollers and iii which serve tosqueeae a further amount of water from the product. The water flowslengthwise'along the rolls in the channel above the line at which therollers meet and spills into a drain, not shown. The product, afterpassing between the rollers 30 and 3|, drops onto the conveyor belt 32which carries it to the bin 35. At this point in the process the productusually retains between 20 and 35 per cent by weight of moisture.

The partially dried granular product is periodically withdrawn into theoven 31. The same bin .may be, and preferably is, used to supply thepartially dried product to a plurality of such ovens. When the oven ischarged, usually about half full, with the product, the lid 39 ofmanhole 38 is closed, the oven is rotated and a heating fluid, e. g. hot

water, heated air, or steam, etc., is introduced I tures between 70-duced to less than tween 80 and 90 ternal vapor pressure the oventhroughthe manhole 38.

, though a stabilizing agent is preferably added.

sulphate, etc., may be used. to effect the coagulaf tion.

The coagulated product is swept from chamber 20 along with theoverflowing liquid onto the moving screen belt 25. It is carried by thebelt between the soft rollers 28 and 29, which serve to. squeeze a largepart, of the water from the product. If desired, the product on the beltmay parent thatinstead of the belt The dry, granular product may becompounded directly with usual rubber compounding agents, e. g.-carbonblack, fillers, sulphur or other vulcanizing agents, etc'uand be shapedand cured to obtain final rubber-like products or it may be molded orrolled into blocks, sheets, or crepe,

'etc., suitable for shipment in uncured condition to manufacturers ofthe finished articles.

The above-described method and/or apparatus may be modified or; changedwithout departing from the invention. For instance, alto the emulsifiedproduct prior to coagulating the latter, such addition of a stabilizingagent is not essential to the invention. It will also be ap- 25 passingbetween the single pair of rolls 28 and 29, it may be passed between twoor more -of such pairs of rolls so as to repeatedly squeeze water fromthe material on the belt, and that prior to passage between the last ofsuch pairs of rolls the material on the belt may be washed with water orother liquid. Still other ways in which the process or apparatus may bemodified will be apparent to those skilled in the art.

Other modes of applying the principle of the invention may be employedinstead of those ex-, plained, change being made as regards the methodherein disclosed provided the step or steps stated by any of thefollowing claims or the equivalent of such stated step or steps beemployed.

I therefore tinctly claims as my particularly point out anddisinvention:

from bin 35 and charged whereby coagulated material is carried from saidvessel together with the overflowing liquid, feed! the coagulatedproduct, ing water from the product.

2. In a method for recovering from an aqueous emulsion thereof asynthetic rubbery polymeric product which is composed at least in partof a chemically combined aliphatic conjugated diolefine and product, theproduct.

3. In a method for while stirring the mixture to cause the copolymer tocoagulate as small irregular shaped pieces having an appearance similarto thatv of in which the coagulation is carried out, whereby coagulatedmaterial is carried from said vessel together with the overflowingliquid, feeding the overflow onto a moving surface which is perforatedso as to permit Water to drain readily from the coagulated product, andcontinuously pressing a further amount of water from the product.

4. In a method for recovering from an aqueous emulsion thereof asynthetic rubbery co-polymer of a conjugated diolefine, which cohesivewhen permitted to stand without agitation while wet'with Water, thesteps which consist in passing the emulsion and a substantiallynon-reactive water-soluble salt capable of coagulating the emulsion intoadmixture with one another while stirring the mixture to cause thecopolymer to coagulate as small irregular shaped pieces having anappearance similar to that of cottage cheese, continuing theseoperations to cause an overflow of themixture from the vessel in whichthe coagulation is carried out, whereby product by heating the same atsub-atmospheric pressure to a temperature between to 5. In a method forrecovering from an aqueous emulsion thereof a synthetic rubberyco-polymer of a conjugated diolefine, which copolymer is withoutagitathe emulsion and a substantially non-reactive water-soluble saltcapable of coagulating the emulsion into admixture with one anotherwhile stirring the mixture to cause the co-polymer to coagulate as smallirregular shaped ROBERT R. DREISBACH.

copolymer is

